Antibodies specific for carcinogen-DNA adducts have probed the nature, extent, and consequences of in vitro and in vivo DNA modification. DNAs substituted with 2-acetylaminofluorene (AAF), benzo[a]pyrene (BP), or cis-diamiminedichloro-platinum II (cis-DDP) were analyzed by quantitative immunoassays able to detect one adduct in one hundred million nucleotides, and by immunohistochemical procedures developed to localize adducts in situ. In hepatic DNA of rats fed a carcinogenic dose of AAF for 4 weeks, adduct accumulation reached a plateau at 2-3 weeks and adducts were shown by immunohistochemistry to be primarily localized in the periportal areas. During 4 subsequent weeks on control diet, adduct removal was biphasic. A computer-derived pharmacokinetic model consistent with this data proposed that adducts are formed into two genomic compartments, one from which adducts are removed rapidly and another from which they are removed slowly. In contrast to the high levels of AAF adducts formed in rat liver DNA, at least 50-fold lower adduct quantities were formed in the DNA of mouse epidermis and cultured mouse epidermal cells exposed to initiating doses of BP. When activated forms of both carinogens were utilized in the keratinocyte focus assay N-acetoxy-AAF yielded more adducts per molar concentration than the BP derivative but no differentiation-altered foci formed in N-acetoxy-AAF treated cultures. Nucleated peripheral blood cell DNA was obtained from cancer patients at multiple times during courses of cis-DDP therapy, and a total of 223 samples were analyzed. Of these, 23 untreated control samples were negative, and 46% of the 200 samples from patients receiving cis-DDP were positive. Adduct accumulation, in positive patients, occurred as a function of total cumulative dose, suggesting relatively slow adduct removal. Disease response data on 47 patients indicated that individuals with adduct levels greater than 200 attomoles/Mug DNA have a very high (65%) rate of complete response to therapy. Parallel experiments in animal models have demonstrated that the same adduct forms in kidney, gonads, and tumors of rats and mice in direct relation to dose.